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First responders, officials and families of 9/11 victims are embracing the news that Osama bin Laden was killed by U.S. forces, but many say they are anxious that his death could endanger New York and America by re-energizing terrorists.

"I understand that people are feeling joyful," said Carl Asaro Jr., who lost his father, "but at the same time I don't want it to incite any further violence."

NYC Celebrates

Images of Americans in New York and other cities were broadcast around the world after the death of the terror mastermind.

Mayor Bloomberg, while citing the significance of the moment, warned that New York City remains a top target and "the killing of bin Laden will not change that."

Raw Video: Bloomberg, Kelly on Security in NYC

Mayor Bloomberg and Police Commissioner Ray Kelly discuss the state of security in New York City after Osama bin Laden's death. MTA's Jay Walder also weighs in. (Published Tuesday, Feb 28, 2012)

Margaret Mauro, whose sister was killed, said bin Laden's death "doesn't mean that the war on terror is over."

"We need to keep our guard up," she said. "We don't know how many terrorist sleeper cells are out there. That's what scares the living daylights out of me."

Former Mayor Rudy Giuliani said in an interview that for the short term, "this could be very dangerous for us."

"In the long run, this is a very very good development in the war against Islamic extremist terrorism," Giuliani added. "He was a major symbol and you cannot underestimate the value of taking out a major symbol like that, but in the short run, this could create problems for us that we have to be very alert to.”

Sheila Langone, who lost two sons, Peter, a firefighter, and Tommy, a police officer, said the killing of bin Laden was "a boost that this country sorely needed."

"This doesn't mean this country is out of danger yet -- we will have to be ever-vigilant," she said.

Kathy Healy, who lost her brother Paul Hamilton Geier, said her family was grappling with mixed emotions. Her 14-year-old niece, who lost her father as a small child, was upset and crying, and the family was concerned about retaliation attacks, she said.

"Unfortunately we have to worry about someone else trying to take his place," he said.

Geoffrey Kohart, father of Cantor Fitzgerald worker Ryan Kohart, said he believes more attacks are possible but hopes the never-ending search for bin Laden sent a message.

"I think it says to the people who want to do these horrible things to the U.S. that it's serious business," he said. "I think they will take more shots at us, but the American people are strong and our resolve is strong."